Influence of Ni/Mo Ratio on Structure Formation of Ni–Mo Complex Compounds in NiMo/Al2O3 Catalysts for Selective Diene Hydrogenation

Fluid catalytic cracking (FCC) gasolines are the most important components of blend gasolines. They are characterized by high octane number due to the great amount of olefins in their composition. However, one of the problems concerning FCC gasolines is the necessity of selective removal of diolefins, which can cause deactivation of catalysts for FCC gasoline hydrofining. In spite of the fact that NiMo/γ-Al2O3 catalysts are usually used in the industrial process of selective diene hydrogenation, literature data on the influence of NiMo catalyst composition on the catalytic performance in selective diolefins hydrogenation are poorly covered. Therefore, the main goal of the present work was to clarify the aspects of the effect of NiMo/γ-Al2O3 catalyst composition on their catalytic properties. The main feature of the catalysts was the higher Ni/Mo molar ratio (0.5 to 2) compared to those for the hydrotreating catalysts. The impregnating solutions, the support, and the catalysts were studied by nitrogen adsorption–desorption, attenuated total reflection Fourier transform infrared spectroscopy, Raman spectroscopy, UV–vis diffuse reflectance spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectra. It was found that the increase in the Ni/Mo molar ratio from 0.5 to 2 resulted in the formation of the mixture of complex compounds like Ni–citrate, Mo–citrate, and NiMo–citrate complexes. It further influences the formation of the sulfide active component; especially, there is a decrease in the interaction of active metals with the support due to implementation of Ni to the support structure. It was found that the excess nickel in the catalysts also contributed to the greater promotion of MoS2 particles and the formation of bulk nickel sulfide particles. It was shown that the higher the Ni/Mo molar ratio, the higher the activity in selective isoprene hydrogenation, while selectivity did not depend on the molar ratio of active metals. The highest activity in isoprene hydrogenation was obtained for Ni/Mo molar ratio = 2.